As the critical dimensions of integrated circuits continue to shrink, the fabrication of gate electrodes for complementary metal-oxide-semiconductor (CMOS) transistors has advanced to replace silicon dioxide and polysilicon with high-k dielectric materials and metals. A replacement metal gate process is often used to form the gate electrode. A typical replacement metal gate process begins by forming a sacrificial gate oxide material and a sacrificial gate between a pair of spacers on a semiconductor substrate. After further processing steps, the sacrificial gate oxide material and sacrificial gate are removed and the resulting recess is filled with a high-k dielectric and one or more metal layers. The metal layers can include workfunction metals as well as electrode plug metals.
With technology scaling, the distance between the source and drain regions of a transistor, i.e., transistor channel length, also is reduced. As the channel length is reduced to increase the number of components per chip, short-channel effects arise. Short-channel effects include drain-induced barrier lowering and punchthrough, surface scattering, velocity saturation, impact ionization, and hot electron effect, all of which are detrimental to transistor performance. Short-channel effects are attributed to two physical phenomena: the limitation imposed on electron drift characteristics in the channel; and the modification of the threshold voltage due to the shortening channel length. Threshold voltage is known to increase or “roll-up” as channel length shrinks
Accordingly, it is desirable to provide integrated circuits having improved high-k dielectric layers and methods for fabricating such integrated circuits. Also, it is desirable to provide integrated circuits having improved replacement metal gates. Further, it is desirable to provide methods for fabricating integrated circuits that provide techniques for selective formation of high-k dielectric layers in replacement metal gate structures. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.